Floating well intervention arrangement comprising a heave compensated work deck and method for well intervention

ABSTRACT

A floating arrangement is provided for overhauling hydrocarbon wells at sea by means of coiled tubing, where the floating arrangement comprises a drill floor and a work deck which is arranged in an opening in the drill floor. The floating arrangement comprises a first set of heave-compensating devices which are arranged for connection to a slip joint connected to a riser in such a manner that an approximately constant tension in the riser can be maintained when the floating arrangement moves in the water. The floating arrangement further comprises a second set of heave-compensating devices which are arranged for connection to the work deck in such a manner that the work deck is at an approximately constant distance from the seabed when the work deck can move relative to the drill floor and the floating arrangement moves in the water. The invention also comprises a method for overhauling hydrocarbon wells at sea from a floating arrangement by means of a coiled tubing frame.

The present invention relates to a floating arrangement device comprising a heave-compensated work deck and a method for implementing a well intervention by means of coiled tubing.

When overhauling hydrocarbon wells, i.e. wells for oil or gas, various tools are employed which are lowered down into the well in a wire line or coiled tubing. Sometimes drill strings are also used in the overhauling process. When overhauling wells located under a fixed installation at sea, this overhauling procedure may be carried out from the fixed installation or a dedicated floating arrangement specially designed for performing interventions on hydrocarbon wells.

When overhauling a well at sea with a floating arrangement according to the prior art, a riser is usually placed between the well and the floating arrangement. On account of the sea's movements, the floating arrangement will usually have at least a partially vertical movement in the water, and in order to avoid damage to the riser it is important to prevent this vertical movement from being transferred to the riser. For this purpose heave compensators are employed which are attached to the floating device and the riser, keeping the riser at constant tension independently of the floating arrangement's vertical movement. This means that the end of the riser is at rest, while the drill floor on the floating arrangement has a vertical movement as a result of the wave motion in the water. The vertical movement of the floating arrangement makes it difficult for personnel located on the drill floor to carry out work on the devices at the end of the riser.

In order to remedy this problem, the applicant has developed a floating arrangement where in an opening in the drill floor a work deck is mounted which is heave-compensated, while the riser is attached to the work deck. This is explained in greater detail in the applicant's Norwegian patent NO 310986 B1.

No dedicated floating devices currently exist for heavy intervention on hydrocarbon wells. In the coming years on the Norwegian shelf there will be a steady increase in the number of hydrocarbon wells of an age that will indicate the need to go in and undertake interventions, either because the wells require maintenance or because production is decreasing as the well grows older, thereby making it necessary to reduce the dimensions of the pipes in the wells.

When undertaking interventions on hydrocarbon wells, use is normally made of coiled tubing which is lowered into the well in order to perform various types of maintenance.

The process of coupling up this coiled tubing, which at present is conducted on floating, oil-producing installations, is considered to be one of the most hazardous operations for the personnel involved. This is due not least to the relative movement between the floating installation and the riser which has no significant vertical motion in relation to the seabed.

Since there will be an increasing need in the future for intervention on hydrocarbon wells, it will also be desirable to have a floating arrangement which is dedicated for carrying out intervention on wells that require it. This will also permit personnel to gain experience more quickly in performing the operations that are necessary for preparations for intervention and the actual intervention. This will soon provide cost savings as experienced people work faster and more safely and a great deal of time is saved. In addition time can be saved when preparing the floating installation for intervention of hydrocarbon wells.

An object of the present invention is therefore to produce a dedicated floating installation which is arranged for implementing rapid connection of amongst other things coiled tubing for intervention on a hydrocarbon well. Another object is to improve the safety of personnel and equipment on the floating arrangement during connection of coiled tubing for intervention on hydrocarbon wells. It is also an object to reduce the time spent in connecting coiled tubing for intervention on hydrocarbon wells.

This is achieved by means of a floating arrangement according to claim 1, a method employed in overhauling hydrocarbon wells at sea, a use of the floating arrangement according to claim 15 and a use of the method according to claim 16. Further embodiments of the invention are indicated in the dependent claims.

Thus a floating arrangement is provided for overhauling hydrocarbon wells at sea by means of coiled tubing, where the floating arrangement comprises a drill floor and a work deck which is arranged in an opening in the drill floor. The opening may be a closed opening or a recess in the drill floor. The floating arrangement comprises a first set of heave-compensating devices which are arranged for connection to a slip joint connected to a riser in such a manner that an approximately constant tension in the riser can be maintained when the floating arrangement moves in the water. The floating arrangement further comprises a second set of heave-compensating devices which are arranged for connection to the work deck in such a manner that the work deck is at an approximately constant distance from the seabed, where the work deck can move relative to the drill floor and the floating arrangement moves in the water.

When carrying out an intervention of a hydrocarbon well it will be desirable to employ a high-pressure riser through the slip joint, so that a high-pressure riser is provided all the way from the top down to the bottom. This is to enable all types of intervention to be conducted from the floating arrangement.

Furthermore the drill floor and the work deck are preferably provided with rail devices, thereby enabling a coiled tubing frame to be moved from the drill floor on to the work deck. The coiled tubing frame may be stored on the drill floor, and can be moved by means of rails out on to the work deck which is then secured to the drill floor by means of hydraulic lock bolts or other suitable devices capable of securely locking the work deck.

The first set of heave compensators may comprise two ore more separate heave compensators which may be mounted on the drill floor, where the heave compensators comprise wires or telescopic connections which can be connected to the slip joint connected to the riser. The heave compensators may also be mounted at other points on the floating arrangement if so desired.

The heave-compensated work deck may be connected to two or more heave-compensating devices via wires or hydraulic cylinders. The heave-compensating devices are preferably also mounted on the drill floor, but may also be mounted at other points on the floating arrangement if so desired.

The work deck is preferably arranged so as to be able to be locked in a fixed position relative to the drill floor by means of, as mentioned above, one or more securing devices provided in the work deck and/or the drill floor. The work deck may therefore be locked in a given position relative to the drill floor, or it may be heave-compensated, which basically means that the work deck does not move vertically relative to the seabed while the drill floor naturally follows the floating arrangement's vertical movements in the water.

In order to control the relative movement of the work deck relative to the drill floor and the rest of the floating arrangement when the work deck is heave-compensated, the floating device preferably comprises control devices which control the work deck's substantially vertical movement relative to the drill floor. These may be rails or the like which are securely mounted or attached to the floating arrangement.

In an embodiment of the invention the first set of heave-compensating devices and the second set of heave-compensating devices are arranged to be able to heave-compensate the slip joint device/the riser and the work deck respectively independently of each other. This is necessary during the preparations for coupling up coiled tubing for intervention on a hydrocarbon well before it is connected to a high-pressure riser passing through the slip joint to the surface blow-out preventer, where during the intervention the coiled tubing frame will be arranged on the work deck.

The first set of heave-compensating devices and the second set of heave-compensating devices are also arranged for synchronous heave compensation of the slip joint/the riser and the work deck. This is necessary when the connection has taken place.

A method is also provided for overhauling hydrocarbon wells at sea from a floating arrangement by means of a coiled tubing frame, where the floating arrangement comprises a drill floor and a work deck and where the work deck is arranged in an opening in the drill floor. The floating arrangement further comprises a first set of heave-compensating devices which can be connected to a slip joint, and a second set of heave-compensating devices which can be connected to the work deck. A riser is furthermore prepared for receiving coiled tubing, whereby at least

-   -   a surface blow-out preventer is mounted on the riser,     -   the slip joint is mounted on the upper end of an upper riser,         where the upper riser is mounted at its lower end on the top of         the surface blow-out preventer,     -   the work deck is secured in a fixed position relative to the         drill floor in such a manner that the work deck is located on         approximately the same level as the drill floor, and     -   the first set of heave-compensating devices are connected to the         slip joint in such a manner that a constant tension in the riser         is maintained when the floating device moves in the water.

Before starting the connection and preparation processes for an intervention, therefore, a constellation is obtained where the work deck is locked in a fixed position relative to the drill floor and at the same level as the drill floor, thereby enabling the coiled tubing frame to be moved over on to the work deck. A high-pressure riser extending from the seabed is connected to a surface blow-out preventer. On the top of the surface blow-out preventer it is connected to a riser extending up to the slip joint. The slip joint, and thereby also the riser, is heave-compensated by the first set of heave-compensating devices.

Thus the method for coupling up the coiled tubing frame and preparing the floating device for an intervention on the hydrocarbon well comprises the following steps:

-   -   lowering one or more lengths of a high-pressure riser from the         work deck through the slip joint and the upper riser down         towards, but not all the way down to the surface blow-out         preventer,     -   moving the coiled tubing frame from the drill floor on to the         work deck     -   releasing the work deck so that it is located in         heave-compensated mode, and     -   lowering the work deck and the high-pressure riser down to the         surface blow-out preventer until the high-pressure riser engages         with and is locked to the surface blow-out preventer.

A further step in the method comprises suspending the high-pressure riser in the work deck before the coiled tubing frame is moved from the drill floor on to the work deck.

It will also be advantageous to move a surface Christmas tree from the drill floor on to the work deck before or together with the coiled tubing frame, and for the high-pressure riser to be mounted to the surface Christmas tree.

A further step in the method comprises attaching a block to the coiled tubing frame before the work deck is released and lowered, with the result that at least a part of the weight of the work deck and the riser is supported by the block.

Alternatively, the work deck may be released and lowered so that at least a part of the weight of work deck and riser is supported by the second set of heave-compensating devices connected to the work deck.

A further step in the method is to arrange for the first set of heave-compensating devices for the slip joint/riser and the second set of heave-compensating devices for the work deck to compensate synchronously when the high-pressure riser and the surface blow-out preventer are interconnected.

The invention also comprises a use of a floating arrangement according to one of the claims 1-8 during intervention of a hydrocarbon well at sea, together with a use of a method according to one of the claims 9-13 during intervention of a hydrocarbon well at sea.

A non-limiting embodiment of the invention will now be described with reference to the attached figures, in which

FIG. 1 illustrates a section of the floating arrangement where the work deck is connected to the drill floor.

FIG. 2 illustrates the same section as in FIG. 1, but where the work deck is released and lowered, together with the high-pressure riser, down to the surface blow-out preventer, where the high-pressure riser and the surface blow-out preventer are interconnected and locked together.

FIGS. 3 and 4 illustrate the same section as in FIGS. 1 and 2, but where the work deck, the high-pressure riser, the slip joint and the surface blow-out preventer are now interconnected and moving synchronously.

FIG. 5 illustrates a section of FIG. 1.

FIGS. 6 to 8 illustrate a perspective view of three different stages of the connection process.

In FIG. 1 a section is illustrated of a floating device 10 comprising a main deck 12 and a drill floor 14. In an opening 13 (see FIGS. 2-4) in the drill floor, a work deck 14 is provided which can move vertically relative to the drill floor 14. The figure illustrates how a coiled tubing frame 20 is moved on to the work deck together with a surface Christmas tree 21.

Below the main deck 12 a high-pressure riser (not shown in the figures) extends up to a surface blow-out preventer 30. To the surface blow-out preventer 30 a riser 32 is connected which is connected at its upper end to a slip joint 36 with an external cylinder 38 and an internal cylinder 39. On the drill floor 14 a heave compensator 16 is mounted which is connected by wires 17 to a connecting device 40 on the slip joint's 36 external cylinder 38. A set of at least two such heave compensators 16 will normally be provided to ensure that the slip joint and the riser are heave-compensated. Heave compensators are similarly connected to the work deck 15, but this is not illustrated in FIGS. 1-5.

One or more lengths of a high-pressure riser 34 are lowered from the work deck down through the slip joint 36. As many lengths are lowered as are necessary to enable the high-pressure riser 34 to reach almost right down to the surface blow-out preventer 30, but not so far down that it bumps into the surface blow-out preventer 30 when the floating arrangement 10 moves vertically in the water on account of the wave movements. This is indicated by the distance 41 in FIG. 1. The slip joint's 36 internal cylinder 39 and the high-pressure riser 40 are connected to the work deck 15.

In FIGS. 2-4 the same section is shown, but with a slightly different sequence in the connecting process. The same design features as described above will therefore not be described again.

In FIG. 2 the work deck 15 is released and is now heave-compensated by heave compensators (not shown in FIGS. 1-5) which are not the same heave compensators 16 which are connected to the slip joint 36.

The work deck with the high-pressure riser 34 are now lowered in a controlled manner to the surface blow-out preventer 30 until they engage with each other and are interconnected by means of known connecting devices. This is illustrated in FIG. 2. When the connecting process is completed, a high-pressure flow channel is created from the seabed up to the floating arrangement.

Finally, in FIGS. 3 and 4 it is shown that the work deck 15 and the high-pressure riser 40 with surface blow-out preventer 30 and the slip joint 36 are heave-compensated. The set of heave compensators 16 which are connected to the slip joint 36 and the set of heave compensators which are connected to the work deck 15 now work synchronously with the result that the work deck 15 and the rest of the chain are equally heave-compensated.

FIG. 5 is a section of FIG. 1 which more clearly illustrates the slip joint 36 with the external cylinder 38 and the internal cylinder 39. The external cylinder 38 is provided with the connecting device 40 to which the wire 17 is coupled. The high-pressure riser passes through the slip joint 36.

In FIGS. 6-8 a larger part of the floating arrangement is shown. The three figures illustrate three steps in the preparations for an intervention of a hydrocarbon well. In FIG. 6 a coiled tubing frame 50 is still located on the drill floor. The work deck 15 is connected to the drill floor. Half of a first set of heave compensators 16 is connected to the slip joint and half of a set of heave compensators 22 is connected to the work deck 15. In FIG. 7 it can be seen that the coiled tubing frame 50 is moved on to the work deck 15. From here the sequence continues as explained in connection with FIGS. 1-5 above. In FIG. 8 it is shown that the work deck 15 is released and the heave compensators 22 now ensure that it is heave-compensated. The following sequence will be to lower the work deck 15 with the high-pressure riser 34, which is passed through the slip joint 36, almost down to the surface blow-out preventer 30 (not shown in FIGS. 6-8), until the high-pressure riser 34 and the surface blow-out preventer 30 are engaged and interlocked.

It should be mentioned that only half of the heave compensators are clearly illustrated in FIGS. 6-8. The remaining half of both sets is located on the opposite side of the work deck. 

1. A floating arrangement for overhauling hydrocarbon wells at sea by means of coiled tubing, which floating arrangement comprises a drill floor and a work deck which is arranged in an opening in the drill floor, wherein the floating arrangement comprises a first set of heave-compensating devices which are arranged for connection to a slip joint connected to a riser such that an approximately constant tension in the riser can be maintained when the floating arrangement moves in the water, and that the floating arrangement further comprises a second set of heave-compensating devices which are arranged for connection to the work deck such that the work deck is at an approximately constant distance from the seabed when the work deck can move relative to the drill floor and the floating arrangement moves in the water.
 2. A floating arrangement according to claim 1, wherein the drill floor and the work deck are provided with rail devices, thereby enabling a coiled tubing frame to be moved from the drill floor on to the work deck.
 3. A floating arrangement according to claim 1, wherein the first set of heave compensators comprises two or more separate heave compensators which are mounted on the drill floor, where the heave compensators comprise wires or telescopic connections which can be connected to the slip joint connected to the riser.
 4. A floating arrangement according to claim 1, wherein the heave-compensated work deck is connected via the wires or hydraulic cylinders to two or more heave-compensating devices.
 5. A floating arrangement according to claim 1, wherein the work deck is arranged so that it can be locked in a fixed position relative to the drill floor by means of one or more securing devices provided in the work deck and/or the drill floor.
 6. A floating arrangement according to claim 1, wherein the floating arrangement comprises control devices which control the work deck's substantially vertical movement relative to the drill floor.
 7. A floating arrangement according to claim 1, wherein the first set of heave-compensating devices and the second set of heave-compensating devices are arranged to be able to heave-compensate the slip joint device/riser and the work deck respectively independently of each other.
 8. A floating arrangement according to claim 1, wherein the first set of heave-compensating devices and the second set of heave-compensating devices are arranged for synchronous heave compensation of the slip joint/the riser and the work deck respectively.
 9. A method employed in overhauling hydrocarbon wells at sea from a floating arrangement by means of a coiled tubing frame, where the floating arrangement comprises a drill floor and a work deck, which work deck is arranged in an opening in the drill floor, and where the floating arrangement further comprises a first set of heave-compensating devices which can be connected to a slip joint, and a second set of heave-compensating devices which can be connected to the work deck, and where a riser is prepared for receiving coiled tubing, whereby at least a surface blow-out preventer is mounted on the riser, the slip joint is mounted on the upper end of an upper riser, which upper riser is mounted at its lower end to the top of the surface blow-out preventer, the work deck is secured in a fixed position relative to the drill floor such that the work deck is located on substantially the same level as the drill floor, and the first set of heave-compensating devices is connected to the slip joint such that a constant tension in the riser is maintained when the floating device moves in the water, wherein the method comprises the following steps: lowering one or more lengths of a high-pressure riser from the work deck through the slip joint and the upper riser down towards, but not all the way down to the surface blow-out preventer, moving the coiled tubing frame from the drill floor on to the work deck, releasing the work deck so that it is located in heave-compensated mode, and lowering the work deck and the high-pressure riser down towards the surface blow-out preventer until the high-pressure riser engages with and is locked to the surface blow-out preventer.
 10. A method according to claim 9, wherein the high-pressure riser is suspended in the work deck before the coiled tubing frame is moved from the drill floor on to the work deck.
 11. A method according to claim 9, wherein a surface Christmas tree is moved from the drill floor on to the work deck before or together with the coiled tubing frame, and that the high-pressure riser is mounted to the surface Christmas tree.
 12. A method according to claim 9, wherein a block is attached to the coiled tubing frame before the work deck is released and lowered, with the result that at least a part of the weight of the work deck and the riser is supported by the block.
 13. A method according to claim 9, wherein the work deck is released and lowered so that at least a part of the weight of the work deck and the riser is supported by the second set of heave-compensating devices connected to the work deck.
 14. A method according to claim 9, wherein the first set of heave-compensating devices for the slip joint/the riser and the second set of heave-compensating devices for the work deck compensate synchronously when the high-pressure riser and the surface blow-out preventer are interconnected.
 15. A method of using the floating arrangement according to claim 1, comprising the step of using the floating arrangement during intervention of a hydrocarbon well at sea.
 16. The method according to claim 9, further comprising the step of performing the method during intervention of a hydrocarbon well at sea. 